The words fliers, flyers sound the same but have different meanings and spellings. Why do fliers, flyers sound the same even though they are completely different words?
The answer is simple: fliers, flyers are homophones of the English language.
Plural form of flier.
Plural form of flyer.
Third-person singular simple present indicative form of flyer.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.